a) Field of the Invention
The invention describes a compact unit for changing the chirp state (temporal sequence of spectral components) of short laser pulses.
b) Description of the Related Art
The use of short-pulse lasers in two-photon laser microscopy is known from U.S. Pat. No. 5,034,613. The coupling of light from a laser light source into a confocal scanning beam path via light-conducting fibers is known, per se, from U.S. Pat. No. 5,161,053.
Generally, short pulses undergo a change in (including a lengthening of) their pulse duration when passing through dispersive media due to the phenomenon of group velocity dispersion (GVD). In addition, nonlinear optical phenomena (e.g., self-pulse modulation, Brillouin scattering, Raman scattering, etc.) which affect the spectral composition of short pulses can attain practical relevance in the dispersive medium due to the high pulse peak outputs and pulse intensities which go along with short pulses.
It is suggested in "Handbook of biological confocal microscopy", pages 447, 448, to compensate for the GVD in optical glass by means of prism arrangements or grating arrangements. However, it is questionable whether this brings about any improvement in view of the complex adjustment problems and wasted energy.